In the sunset of his career, Penn returned as a Welterweight to successfully complete his trilogy with Matt Hughes, before retiring between two losses and a draw in attempts to regain the UFC Welterweight Championship. In pursuit of a career resurgence with a descent into the Featherweight division, Penn conclusively announced his retirement following another loss to Frankie Edgar.

UFC President, Dana White credits Penn as the man who brought the lower weight divisions into the mainstream of mixed martial arts; claiming Penn to be "the first crossover pay-per-view star for the Ultimate Fighting Championship's lighter weight divisions",[12][13] as well as that "[through his] accomplishments, B.J. Penn built the 155-pound division".[14] Credited as the greatest Lightweight combatant in mixed martial arts history, Penn's domination of the division, as well as his performances in higher weight classes have him regarded as one of the greatest fighters in the history of the sport.[15]

Penn was born in Hilo, Hawaii, USA to Jay Dee Penn, an American, and Loraine Shin, a Korean-American.[16] At the age of 17, Penn began training in Brazilian Jiu-Jitsu after being introduced to it by his neighbor, Tom Callos.[17] Callos had put up fliers in local gyms looking for people to train with,[18] and B.J.'s father Jay Dee Penn had called Callos and said his boys were interested.[17] Callos then taught B.J. and his brother what he knew.[18] Shortly thereafter, B.J. moved to San Jose, California to begin training at the Ralph Gracie BJJ academy with Dave Camarillo, who he lived with and became close friends with. It was here during his time in San Jose that he decided to pursue a career in martial arts (albeit not mixed martial arts at the time).

In 1997 Penn began training Brazilian Jiu-Jitsu under Ralph Gracie, eventually earning his purple belt from Gracie.[19] At that point he moved to Nova União where he was eventually awarded his black belt in 2000 by Andre Pederneiras.[19] A few weeks later he became the first non-Brazilian to win the black-belt division of the World Jiu-Jitsu Championship held in Rio de Janeiro, Brazil.[20] While Penn's most well-known and prestigious achievement was placing first in the black belt division in the 2000 world championships, he had success at the Mundials in previous years. In 1999, at the age of 20, Penn finished 3rd, earning himself a bronze medal in the brown belt division, losing only to Fernando "Tererê" Augusto, and in 1998, earned a silver medal, placing 2nd in the blue belt division.[21] Penn is thought to have earned the fastest legitimate black belt of all active Brazilian Jiu-Jitsu practitioners.[22]

Penn received his first UFC Championship in 2004 at UFC 46: Supernatural. Penn jumped up in weight classes to challenge the five-time defending UFC Welterweight ChampionMatt Hughes to fill a title contention slot in a division where Hughes had already defeated all the available opposition.[25] Heavily favored to win, Hughes lost the fight four minutes into the first round by rear naked choke after giving up his back with only 23 seconds left in the round, in a bout which remains as one of the biggest upsets,[26] as well as one of the greatest submission victories in mixed martial arts history.[27]

Penn signed to exclusively fight for the Japanese Fighting and Entertainment Group's (FEG) K-1 promotion citing a lack of challenging fights left for him in the UFC.[21] The UFC promptly stripped him of the welterweight title, claiming Penn breached his contract and that the signing constituted him refusing to defend his title. Penn filed a suit against the UFC and publicized his side of the conflict, claiming his UFC contract had already expired. Penn filed a motion to stop the UFC from awarding a new welterweight title, but that motion was denied.[28]

In his second fight for FEG, Penn fought again at welterweight (170 pounds) and defeated Duane Ludwig at the 2004 K-1 MMA Romanex show in under five minutes by arm triangle choke.[2] Following the Ludwig fight, Penn moved up in weight class to face the undefeated Rodrigo Gracie at middleweight (185 pounds).[29] Penn won by decision, extending his winning streak to four fights.[19] On March 26, 2005, at the inaugural event of FEG's new MMA promotion Hero's, Penn faced future UFC Light Heavyweight ChampionLyoto Machida, losing by unanimous decision at K-1 Hero's 1. The fight happened at an open weight class with Penn weighing in at 86.5 kilograms (191 lb) and Machida 102 kilograms (225 lb).[30] Later that year at K-1 World Grand Prix Hawaii, Penn returned to middleweight to face Pride Fighting Championship veteran Renzo Gracie, which he won by unanimous decision.[2]

In early 2006 at UFC 56, UFC president Dana White announced that Penn and the UFC had agreed to a settlement and Penn was to return as a top welterweight contender. Penn re-debuted on March 4 at UFC 58, losing to Georges St-Pierre by split decision in a fight that determined the number one welterweight contender. Although St. Pierre was declared the winner after a three round decision, some believed that Penn had done enough to earn himself the victory, causing noticeably more damage throughout the fight, as Joe Rogan described Georges St-Pierre’s face being "a bloody mess" while B.J. Penn "barely having a scratch on him." Despite having lost the bout, Penn's performance against Georges St-Pierre, is considered to be one of the best put forth against the future UFC Champion.[31]

After new top contender St. Pierre injured himself during training, the UFC announced that Penn would replace St. Pierre in an upcoming title fight, setting up a highly anticipated rematch with Hughes for UFC 63 on September 23, 2006.In the bout, Penn controlled the first two rounds, but sustained a rib injury during the scramble to take Hughes' back in round two. He was visibly different in the third round, appearing exhausted and missing punches he was landing earlier. Hughes was able to take Penn to the mat, and in side control crucifix position rained punches on Penn's head until referee "Big" John McCarthy stopped the fight at 3:53 of the third round, making this the first time that Penn had been stopped in a fight. In an interview found on Penn's personal website, Penn stated that by round three he could hardly breathe and had no "mobility in his core."[32] Despite the injury, Penn congratulated Hughes, calling him a great fighter and saying he deserved the victory.

Penn was a coach for The Ultimate Fighter 5, which aired on April 5, 2007.[33] Penn lead a team of eight lightweight fighters, and fought a rematch against Jens Pulver at the conclusion of the series on June 23, 2007.[34] He won with a rear naked choke in the second round after controlling Pulver from the mount and then taking Pulver's back.[35] Although he held the choke for a moment after Pulver tapped out,[36] the two then embraced,[36] with both later saying they no longer held any ill will against each other.[34]

On July 7, 2007, during the post-fight press conference of UFC 73, UFC president Dana White announced that Penn would stay at lightweight to fight current UFC lightweight champion Sean Sherk. However, Sean Sherk subsequently was suspended by the California State Athletic Commission, and the status of the possible title fight was left in limbo as he pursued his appeals.[37] With Sherk's title status still in limbo after months of hearings, the UFC scheduled Penn to fight Joe Stevenson at UFC 80 on January 19, 2008 for an interim lightweight title.[38] The subsequent final decision by the California State Athletic Commission, which did not overturn Sherk's suspension, led to the title being stripped from Sherk and the Penn-Stevenson fight being upgraded to a full title bout,[39] with the winner facing Sherk in their first defense.

Penn knocked Stevenson down seconds into the first round with a right uppercut, then took Stevenson down, delivering a well placed elbow from the top position that inflicted a serious cut near Stevenson's hairline.[40] In the second round, Stevenson fought more aggressively but was still unable to threaten Penn. Penn worked to back mount and defeated him by rear naked choke at 4:02 of the second round to win the Lightweight Championship. He celebrated the win by licking Joe Stevenson's blood off of his gloves. The win for Penn was awarded Beatdown of the Year by Sherdog for 2008.[41] With this win, Penn became the second man (after Randy Couture) to win UFC titles in two different weight classes.[42]

On May 24, 2008 at UFC 84 at the MGM Grand Garden Arena in Las Vegas, Nevada, Penn fought former champion Sean Sherk in his first title defense bout. The fight was billed by play-by -play commentator Mike Goldberg as the "biggest fight in the history of the UFC lightweight division". Sherk attempted to take Penn down only once (in the first round), instead the fighters traded punches and leg kicks for the remainder of the fight. Penn landed jabs several times, utilizing his reach advantage over Sherk. In the closing seconds of the third round, Penn threw a punch and a hook that backed Sherk into the cage. Sherk then ducked under another punch – possibly to shoot for a takedown – when he was hit in the head by a flush flying left knee from Penn. Sherk went down and Penn continued with strikes, but the round ended before the referee stopped the fight. However, Sherk was unable to continue and Penn was declared the victor by TKO (strikes). After the fight, in response a question by Joe Rogan about his future, Penn asked the crowd if they wanted to see him fight Georges St-Pierre and was answered with a loud ovation.[43] Later, Penn told Fighters Club TV that he would face the winner of UFC 87 Welterweight title fight between Georges St-Pierre and Jon Fitch, which St-Pierre ended up winning by unanimous decision. St-Pierre's victory led to the scheduling of B.J.'s next fight as a Welterweight Championship fight.

Penn challenged Georges St-Pierre for St-Pierre's welterweight title on January 31, 2009, the night before the Super Bowl. The date led UFC 94 to be billed as the "UFC Super Bowl Weekend," and it was anticipated to be the biggest UFC pay-per-view event ever.[44] Before the fight with St-Pierre, Penn made a controversial comment that he was going to try to kill St-Pierre in the ring,[45] but he later explained that he was speaking figuratively.[46]

The first round of the fight was somewhat even, with Penn exercising elusive head movement, fast hands and good take-down defense, thwarting all of St-Pierre's take-down attempts while both exchanged punches. In the ensuing three rounds, however, Penn turned out a lackluster performance. St-Pierre scored his first take-down of the night midway through the second round, and by the end of the round Penn was visibly tired. At the start of round three, St-Pierre landed a "superman punch" that bloodied Penn's nose and shortly took Penn down again. From that point on, St-Pierre took Penn down almost at will, repeatedly passed Penn's renowned guard, and persistently punished the Hawaiian with a ground-and-pound attack.[47] Penn later admitted that he could not recall anything that happened during the 3rd and 4th rounds because "I was probably borderline knocked out or something."[48] At the end of the fourth round, after more of St-Pierre's ground-and-pound onslaught, and upon B.J.'s command, Penn's brother requested that the referee stop the fight. After the fight, Penn failed to attend the post-fight press conference due to having stayed in the hospital.

A controversy arose during the fight as St-Pierre's corner-men were spotted rubbing St-Pierre's back immediately after applying Vaseline to his face. Members of the Nevada State Athletic Commission (NSAC) came into the octagon and wiped St-Pierre's torso down. Penn later sent a formal request to the NSAC, asking them to investigate.[49] Despite all of the complaints by the Penn camp, the NSAC ruled that there was no infraction.[50] This incident was famously coined by Penn fans as the "Greasegate" and remains as one of the biggest controversial moments in UFC history[by whom?].[51]

"I think he absolutely, positively knew that he was rubbing grease on him. Do I think Georges was trying to cheat? Absolutely not at all. But that corner man was rubbing grease on him." -Dana White, post fight at UFC 94.[52]

The rules of the UFC were modified so that only the official "cut men" would be allowed to have or apply Vaseline to the fighters. The procedures governing the transition from the fighters walk-in to the cage and while in the cage were also changed. Previously, fighters would walk up next to the cage, see the cut man who would apply Vaseline, be checked by the referee, and then have an opportunity to speak with or hug their coaches or cornermen before entering the cage. To prevent an opportunity for the fighters to have Vaseline applied illicitly, fighters now must first part from any company, have Vaseline applied by the cut man, be checked by the referee, and then go directly to the cage. Finally, no cornermen will be allowed to have Vaseline in the cage between rounds. In this way, the fighter's contact with Vaseline is fully controlled by the cut men and referee, who work independently of the UFC.[53]

UFC President Dana White said that the incident had no effect on the outcome of the fight although he wished the incident had not happened. Penn did, after all, quit after the fourth round. In his first post-fight interview Penn spoke of his belief that if St-Pierre were found to have been "greased" he would lose all respect for him, while admitting that "[I] definitely got my butt kicked."[54] Penn claims that before the match he warned the NSAC that St-Pierre might use grease intentionally.[48] St-Pierre responded to the allegations by offering to fight a rematch against Penn.[55] Penn went on record as accepting the offer for a re-match.[56] Following his informal acceptance of a proposed second rematch, Penn filed a formal complaint with Nevada State Athletic Commission seeking to prevent St-Pierre from fighting by suspending St-Pierre's fighter's license. In addition, Penn unsuccessfully requested the suspension of St-Pierre's cornermen, Greg Jackson and Phil Nurse, a fine of $250,000, and overturning the result of the fight to a no-contest.[57][58]

Penn began negotiations to fight Kenny Florian in the summer of 2009.[48] The Florian-Penn title fight was scheduled for UFC 99, but B.J. Penn requested more time off after his fight with GSP. He defended his title against Florian on August 8, 2009 at UFC 101. Penn looked noticeably in better physical shape than his previous outings at 155 lbs and negated any sort of takedown offense from Florian the entire match despite his opponent's persistence in grappling and engaging the clinch.

On his feet, Penn avoided virtually any damage, constantly stuffing or evading any attempts of a left high kick, punches, or elbows from Florian when the two departed from the clinch. In a measured performance, Penn preferred to pace himself in his standup, occasionally showing explosive bursts of striking up until the fourth round, where he executed a powerful takedown and quickly assumed the half guard position, punishing the contender with elbows until gaining the full mount, where punches followed to continue the ground and pound assault from the BJJ specialist.

A scramble ensued, where Florian gave up his back twice but was unable to escape Penn's mount, the second time Penn took his opponent's back, he looked to trap Florian's arm with one of his legs, but was unable to do so, instead striking the liver of Florian with his heel, which eventually led Penn to secure a rear naked choke at 3:45 of the fourth round to defend his lightweight championship title.

Penn fought Diego Sanchez for the UFC Lightweight Championship on December 12, 2009 at UFC 107.[59] Penn negated virtually any offense from the contender, exercising good footwork and elusive head movement whilst remaining flawless in his takedown defense on 27 attempts from Sanchez. He stalked his opponent for large periods of the match and stunned Sanchez early, dropping him; following up with multiple clean shots, which Sanchez showed good durability in weathering. Penn, showing good conditioning for the duration of the bout, continued to stuff all takedowns, punches and left high kicks from Sanchez and dominated with aggressive bursts of striking throughout. He hurt Sanchez several times, until finally rocking him with a flurry in the final round, swarming to finish the combo with a right high kick. The kick opened up a huge cut on Sanchez's forehead above his left eye, causing the fight to be halted on doctor's advice at 2:47 of the fifth round with a TKO. The victory marked only the second fight in UFC history to end in the fifth round, and also earned Penn the distinction of being the only man to have stopped Sanchez.

"That right there, ladies and gentlemen, is the greatest lightweight, in the history of the sport!" -Joe Rogan, post fight at UFC 107.[60]

The performance marked the third time Penn had successfully finished a fight in defending his UFC Lightweight Championship, setting a new record of lightweight title defenses, by breaking the previous record of two defenses by Jens Pulver.[61] Later during the post-fight press conference UFC President Dana White told the media he was proud of Penn's willingness to take MMA more seriously in his training when earlier he felt Penn had coasted through the UFC solely on natural talent.[62]

Penn's next defense was on April 10, 2010 at UFC 112 against Frankie Edgar. Despite being an overwhelming favorite coming into the fight, Penn lost the closely contested bout by unanimous decision; breaking his eight-year undefeated streak in the lightweight division. 8 of 9 media outlets scored the bout in favor of Penn.[63] After the fight, Penn congratulated Edgar on winning the belt. Despite this, the results garnered much criticism as many disagreed with the judges decision after the five round fight, having believed that Penn had done enough to earn himself the victory.[64] Due to the controversy surrounding the outcome, an immediate rematch with Edgar was scheduled as his first title defense.

"BJ is the greatest lightweight ever. I can just hope to be half the champion he was." -Frankie Edgar, post fight at UFC 112.[65]

Penn fought Edgar in a rematch at UFC 118.[66] Edgar was able to negate his ground offense and control the fight with good movement and striking combinations. All three judges scored the fight 50–45 for Edgar.[67][68]

Penn fought Matt Hughes at UFC 123 in a rubber match after their previous two fights at UFC 46 and UFC 63.[69] Penn defeated Hughes in 21 seconds of the first round by knockout after flooring Hughes with a right hand and following with additional strikes on the mat.[70][71] Penn earned knockout of the night honors for his performance.

Following the UFC 123 post-fight press conference, UFC president Dana White said that Penn would fight top welterweight contender Jon Fitch at UFC 127 in Australia.[73] Penn trained with Matt Hughes and Floyd Mayweather, Sr. in preparation for the fight.[74][75] Penn surprised Fitch by taking him to the ground instead of using his stand up skills. The fight ended in a draw, snapping Fitch's five fight UFC win streak, and Penn stated that he would gladly have a rematch in the future. UFC matchmaker Joe Silva stated that neither the fans nor the UFC are interested in a Penn-Fitch rematch.[76]

Penn was expected to face Carlos Condit on October 29, 2011 at UFC 137.[77] B.J. Penn relocated his camp to Southern California in an effort to prepare for the bout. Penn was joined in California by former UFC middleweight and Ultimate Fighter winner Kendall Grove and B.J.'s brother Reagan Penn, as they both prepared for their August 27 fights on the ProElite show in Hawaii.[78] However, on September 7, Condit was pulled from the bout and replaced Nick Diaz in the main event against Georges St-Pierre.[79] Dana White stated that Penn will fight Nick Diaz in the main event at UFC 137 after GSP pulled out due to knee injury. Penn lost via unanimous decision after winning the first round by crisp boxing as well as mixing in a takedown against the former Strikeforce Welterweight Champion, but was unable to mount any significant offense or defense against Diaz's stand-up attack in the remaining two rounds.

Immediately following the loss to Diaz, Penn announced his plans to retire, saying into the microphone, "Joe, this was probably the last time you'll see me in here. I can't keep performing at the top level. That's it Joe. I got a daughter and another daughter on the way, I don't want to go home looking like this. I'm done."[80] On November 1, Penn posted a message to fans on his website indicating that he plans to take some time off, but the retirement decision is not yet official. He said, "I want to thank all the fans for their love and support. I have decided to take some time off to enjoy life, train and teach. I will keep you guys posted with what’s next."[81] A few months afterwards, B.J. tweeted angrily at both Jon Fitch and Nick Diaz, causing many to believe that Penn would be returning from his retirement within the near future. His manager has stated that the old B.J. is back and could be returning to MMA.[82] In April 2012 UFC president Dana White said B.J. Penn turned down a fight with the reigning Strikeforce Lightweight Champion, Gilbert Melendez, and that Penn wants to continue at 170 pounds "whenever he is ready". White also said he feels that B.J. Penn deserves to be in the UFC Hall of Fame, stating that he was a pioneer for the lightweight division, at a time when many believed that there couldn't be any stars at 155 pounds.[83][84]

Several months after declaring his retirement from mixed martial arts, B.J. Penn announced that he would be returning to the octagon after repeated challenges made by welterweight prospect Rory MacDonald; stating, "Rory, I accept your challenge!".[85] Initially, Penn was expected to face Rory MacDonald on September 22, 2012 at UFC 152.[86] However, MacDonald pulled out of the bout after sustaining a cut to the forehead while training.[87] Penn vs. MacDonald eventually took place on December 8, 2012 at UFC on Fox 5.[88] Penn lost the fight via unanimous decision. After the fight Dana White stated that he'd like to see B.J. Penn retire from mixed martial arts, although Penn has hinted a desire to return to the UFC's lightweight division. Following months of silence regarding his future, Penn spoke with Ariel Helwani in an interview for UFC on Fox, where he admitted that he was still undecided on his future, telling him that "at this moment, my guess is probably a little better than yours, but I don't know, I'm enjoying what I'm doing."[89]

In January 2016, after an 18-month hiatus, the 37 year old Penn announced his intentions to return to active competition with plans to continue in the UFC's featherweight division.[97][98] He was briefly expected to return in April 2016 at UFC 197. However, Penn's return was delayed after an investigation into criminal allegations made against him was launched.[99] In turn, Penn was expected to face Dennis Siver on June 4, 2016 at UFC 199.[100] However, Siver was forced out of the bout in early May with an undisclosed injury.[101] He was replaced by Cole Miller.[102] Subsequently, Penn himself was removed from the card on May 23 after he was flagged for the use of a medically-administered IV during a non-fight period, when the use of IV had been recently banned 365 days a year.[103]

Penn was expected to face Ricardo Lamas on October 15, 2016 at UFC Fight Night 97.[104] However on October 4, Penn pulled out of the fight citing an injury.[105] In turn, the promotion announced on October 6 that they had cancelled the event entirely.[106][107]

His nickname "B.J." is a shortened version of another nickname "Baby Jay", which itself derives from the fact that Penn is the youngest of his brothers all named "Jay Dee Penn".[109] B.J.'s father, who is Irish and English, named 3 of his 4 children "Jay Dee", while the fourth is Reagan. In order to avoid confusion each of the sons named "Jay Dee" goes by a nickname: "Jay", "Jay Dee", and "Baby Jay".[110] Penn's mother, Lorraine Shin, is of Korean descent.

Being born in Hawaii, Penn takes much pride in his Hawaiian upbringing. Penn often plays Hawaiian music during his walk-out entrances, a combination of Hawaii ’78 into E Ala E, both performed by Hawaiian musician Israel Kamakawiwoʻole as a tribute to his Hawaiian heritage and respect for his opponents, fans and the fight game. Penn has also stated that he identifies strongly with his Korean roots and has traveled to Korea to hold seminars. He also said that he gets his hot temper from his Korean side which helps him use this energy in his fights.

Penn has had two daughters with the same mother. He says that they have never married since a large percentage of Hawaiians have children out of wed-lock and "it doesn't matter that much in Hawaii."[111][112] Penn is the co-author of Mixed Martial Arts: The Book of Knowledge, an instructional book on mixed martial arts fighting.[113] Penn, along with Dave Weintraub, authored the autobiography Why I Fight: The Belt is Just an Accessory in 2010. The book debuted at #22 on the New York Times bestseller list.[114] Penn also appeared in the film Never Surrender in 2009.[115]

Since his debut in the Ultimate Fighting Championship, Penn emerged as one of the biggest stars in the history of sport, headlining a total of eleven main-events (nine pay-per-view main-events) for the UFC during the course of his career (in addition to five for K-1). Penn was regarded as one of the most controversial and outspoken players in the history of mixed martial arts whose influence was considered instrumental in popularizing the UFC around the world in the 2000s and 2010s. His impact on the sport went beyond his UFC titles and dominant performances inside the octagon. A longtime advocate for drug testing in the sport, Penn was also the first to introduce an independent foundation in MMA to promote, coordinate and monitor the fight against performance enhancing drugs in sports with the inclusion of Voluntary Anti-Doping Association (VADA) during his and his opponent's training camps.

Recognized for his role in the resurgence of the lightweight division, Penn is considered to have been the division's most influential figure, turning the weight class around (in bouts with Sean Sherk, Kenny Florian, Diego Sanchez, Jens Pulver, and Joe Stevenson) to become one of the UFC's most popular, at a time when they had considered disbanding the division altogether and many publications had questioned whether lighter-weights could be successful.[116][117] His nickname, The Prodigy originates prior to him competing in mixed martial arts, from accomplishing his extraordinary feat in the sport of Brazilian Jiu Jitsu (earning his black belt in just under three years and winning the black belt division in the World Jiu-Jitsu Championship only three weeks later).[118][119] His biography on the UFC website expressed this accomplishment as "an astonishing achievement in a sport where it takes the average athlete ten years or more to reach black belt status.[120]

Penn is regarded amongst the greatest mixed martial artists of all-time. He is widely considered the greatest Lightweight (155 lbs) competitor in the sport's history,[116][124][125][126] in addition to one of the greatest Welterweight (170 lbs) competitors as well (in his performances against Georges St-Pierre and Matt Hughes).[127][128] Penn was also simultaneously ranked number one in both of these divisions following his back-to-back submission victories over Takanori Gomi and Matt Hughes, where he is the only fighter to hold such an honor.[129][130]

During the televised broadcast of UFC 187 in May 2015, it was revealed on Fox Sports that Penn would be inducted into the revamped UFC Hall of Fame under the Modern Category during International Fight week festivities prior to UFC 189.[139]